Stress radiographs have been used for several years to detect the amount of varus/valgus knee laxity in the knee joint. The popularity of radio graphic methods of monitoring the knee joint has, however, been adversely affected by the X-ray exposure of an assistant that performs the stress imaging. They are also used to evaluate the degree of compartmental involvement in degenerative osteoarthritis. The cruciate ligaments are thought to be a secondary stabilization mechanism in the varus/valgus orientation.
Stress X-rays are an essential component of the assessment of a patient with a knee ligament injury. Such X-rays provide an objective measure for determining the extent of an injury prior to surgery; assessing whether a partial ligament tear is healing non-operatively; and in assessing postoperative outcomes. The use of stress X-rays is also necessary to properly diagnose osteoarthritis and most multi-ligament knee injuries. A correct interpretation of acute and chronic ligament injuries or flexion in different angles of the knee is most valuable and many advances have been made in treatment protocols.
Total knee arthroplasty (TKA) has become a common procedure worldwide and each year numerous patients undergo the procedure with differing degrees of success. Similarly, in various arthroscopic cases there is a necessity for a stress view to determine the laxity of the knee joint. One of the pre-requisites for a well-functioning total knee arthroplasty is its proper alignment and stability. Proper alignment is considered as a restoration of the anatomical axis of the femur of between 2.4 and 7.2 degrees of valgus. A body mass index of >41 kg/m2 signifies the risk of failure of a total knee arthroplasty. A recent study showed that a deviation of 1° varus from neutral alignment increases the medial load share by 5%.
Instability is a well-recognized cause of poor functional outcome after total knee arthroplasty. The causes of instability after total knee arthroplasty include inadequate soft tissue balancing; loss of ligamentous integrity; component wear; improper component sizing; and component mal-positioning.
The popularity of radiographic methods of monitoring the knee joint has been adversely affected due to X-ray exposure of the radiographers/health assistants involved; the variability of the stress forces applied; the cost of the equipment; and the size and bulkiness of the equipment.
A standardized protocol for the flexion of a knee requires the knee to be set at various angles from full extension to 120° knee flexion. At times a lateral view X-ray needs to be taken to check whether a particular flexion angle at the instrument is equal to the actual flexion of the femur and tibia.
Initially in various studies, various Varus/Valgus laxity of the knee were measured at extension (0-20° flexion) and 75° flexion. Laxity at extension was measured using a TELOS™ arthrometer while the patient lay in a prone position.
The TELOS™ arthrometer is a device in which a pair of parallel bars supports a central pressure unit and two generally parallel arms extend away from the bars in the same direction. The one arm can receive a foothold whilst the other arm can receive a roller and the pressure unit can exert pressure on a pad between those two items. The arrangement is rather awkward and requires, in some instances, that the patient be orientated in a highly non-ergonomic position. Also there is no possibility of developing any comparative information as regards the patient's other knee. Because of the rather awkward positioning of the patient and the device, a radiographer needs to be present when X-rays are taken.
It is the aim of this invention to provide an anatomical support to facilitate the medical imaging of the hip, leg and especially the knee in which disadvantages perceived of the existing equipment available are diminished at least to some extent.